Dehydrocyclization process



Feb. 27, 1962 D. F. OTHMER ET AL 3,023,254

DEHYDROCYCLIZATION PROCESS Filed Jan. 23, 1958 2 Sheets-Sheet 1 FIGURE I DA [FIN AROMA 77 C5 FEED STOCK PARAFF/N 60 FEED 6T0 CK FIGURE 2 DONALD 1-. OTHMER DENIS K. HUANG IN VENTORS 1962 D. F. OTHMER ET AL 3,023,254

DEHYDROCYCLIZATION PROCESS Filed Jan. 23, 1958 2 Sheets-Sheet 2 AfiOMAT/Cs P W/ M TED 5706A FIGURE 5 WUEL FIGURE 4 DONALD F. OTHMER DEN/S K. HUANG INVENTORS.

United States Patent 3,023,254 DEHYDRQCYCLIZATION PROCESS Donald F. Othmer, Coudersport, Pa., and Denis K. Huang, 99 Livingston St., Brooklyn, N.Y. Filed Jan. 23, 1958, Ser. No. 710,818 6 Claims. (Cl. 260673.5)

This invention relates to the preparation of aromatic hydrocarbons from the corresponding paraflin hydrocarbons by dehydrocyclization.

More particularly it relates to dehydrocyclization using as starting material straight chain hydrocarbons having six or more carbon atoms none of which has more than one branched chain.

According to this invention suitable paraffinic hydrocarbons are vaporized and then catalyzed at or near atmospheric pressure and suitably elevated temperatures.

It is an object of this invention .to produce aromatic compounds from straight chain compounds by removing hydrogen atoms simultaneously with ring formation.

It is another object to prepare benzene from normal hexane and toluene from normal heptane.

It is another object or purpose of this invention to convert normal octane to a mixture of ortho xylene, ethyl benzene and styrene.

It is another object of this invention to convert normal heptane into a mixture of aromatics which contains a substantial amount of benzene. I

It is another object of this invention to convert normal octane into a mixtureof aromatics which contains a substantial amount of toluene and benzene.

These and other objects of this invention will become apparent upon reading the following disclosure taken in conjunction with the accompanying drawing in which;

FIG. 1 is a schematic flow diagram showing a fixed bed procedure for preparing the aromatic compounds according to this invention,

FIG. 2 is another schematic flow diagram showing a moving bed procedure for preparing the aromatic compounds according to this invention,

FIG. 3 is a schematic flow diagram showing a fluidized bed procedure for preparing the aromatic compounds according to this invention and,

FIG. 4 is a schematic view, partly in cross-section, of an isothermal procedure used to prepare aromatic compounds according to this invention and FIG. 5 is a transverse section view taken on line 5-5 of FIG. 4.

This invention process employs as catalyst chromium oxide, or molybdenum oxide, or cobalt molybdate, or platinum metal. The activity of the oxide catalysts may be promoted by the use of neodynium oxide or didymium oxide. The catalyst is preferably deposited on alumina or activated alumina, or on other suitable supporter. Whenever the catalyst is deactivated due to precipitation of carbon thereon, it may be revitalized by burning off the carbon in a stream of oxygen or air suitably diluted if necessary with inert gas.

The dehydrocyclization process of this invention is endothermic and therefore requires heat in order to proceed. This heat requirement may be supplied by superheating the vaporous feed stream above the temperature required to effect dehydrocyclization; or the heat may be supplied by means of an externally heated stream of hydrogen gas which is then mixed with the vaporous "ice feed stream; or the heat requirement may be supplied by suitably heating externally the moving catalyst where moving catalyst is used. Preferably, the heat requirement is supplied by utilizing the heat of the efiiuent flue gas.

The preferred temperature of this invention are 840 F. to 1100" F. The preferred space velocity expressed in terms of volume of liquid feed per volume of catalyst per hour is between 0.3 and 0.7. The pressure used in this invention is preferably at or near atmospheric pressure.

This process is operable in conventional petroleum refineries using suitable petroleum fractions. In such instances the present invention may be used in combination with a conventional isomerization unit to replace the conventional hydroforming unit for the production of aromatic compounds or of a highly aromatic fraction usable as a high octane gasoline. v V

The catalyst size used varies with the procedure em- 'ployed. Thus a particle size of less than one-eighth inch eighth inch and three-sixteenth inches may be most advantageous with the moving bed embodiment of this invention.

In performing this invention for producing benzene the prepared paraflinic feed stock may be vaporized at atmospheric pressure or substantially atmospheric pressure and then the vapors are heated to about 850 F. to 1100 F. and brought into contact with the catalyst. The reacted vapors are then passed through a partial condenser to remove molecules having more than five carbon atoms. The condensate is fractionally distilled to separate the aromatic fraction, the unreacted paraflin fraction, and other products. Other means, for example, solvent extraction, may be used in place of distillation to separate out various fractions from the condensate. Where however a feed consists substantially of normal parafiins simple distillation is effective enough for separating out the various fractions of the condensate.

The inlet temperature of the parafiinc hydrocarbon vapors control the aromatic distribution of the liquid product. By proper regulation of the feed inlet temperatures, products that contain substantial amounts of arcmatics with the same number, or less than the number, of carbon atoms of the corresponding feed charged can be produced.

Regeneration of catalyst in the fixed bed modification of this invention is done by shutting off the vapor feed supply and substituting a stream of air or oxygen suitably diluted with inert gases to prevent overheating of the catalyst bed during the burning of the carbon deposited thereon. Where regeneration of fluidized catalyst is to be accomplished, the spent catalyst is conducted to a con- 'ventional lift line preferably located centrally in the body of the reactor in order to utilize the regeneration heat to supply in part the heat requirement of this inventive process. A lift line temperature of about 1200 F. to 1300 F. may be used for the endothermic reaction of this invention when there is to be a temperature of 840 F. to 1100 F. in the reactor space disposed around the lift line.

This invention will be more easily understood by reference to the drawing showing a plurality of embodiments. Turning to the fixed bed embodiment shown in FIG. 1, the selected paraflinic feed stock is introduced by conduit 1 into a heater 31 heated by conventional means (not shown) where the feed stock is vaporized and superheated to about 1000" F. From the heater 31 the heated feed stock is conducted into reactor 4 through conduits 2 and 3. The gaseous feed is partly converted by suitable catalysts in reactor 4 and it is then discharged into conduit 5. From conduit 5 the vapors are lead into a compressor 6 and compressed.

The compressed vapors are conducted by conduit 7 into heater 31 where they are heated to about 1000 F. The

heated vapors are now conducted by conduit 8 into a second reactor 9, containing a suitable catalyst. The reacted vapors from reactor 9 pass through conduit 10 into a separating drum 11 where hydrogen gas is disengaged and high polymeric materials are separated.

The balance of the stream from drum 11 is conducted through conduit 12 into a fractionating column 13 where low molecular weight hydrocarbon gases are removed through conduit 21, after the usual distillation and rectification operations. The heavy product at the bottom of column 13 consisting of aromatic hydrocarbons and unreacted paraflins is conducted through conduit 14 into a conventional extractive distillation column 15 for separation of the aromatic hydrocarbons from the paraflinic hydrocarbons. The unreacted paraflins are conducted through conduit to conduit 1 and the aromatics are conducted through conduit 16 into a conventional solvent recovery tower 17. The aromatic portion is recovered overhead through conduit 18 and the solvent employed in the extractive distillation is recycled through conduit 19 to the extractive distillation column 15.

Hydrogen gas from separating drum 11 is conducted through conduit 33 to compressor 34 where it is compressed to about 100 pounds per square inch. From compressor 34 a recycle portion of the compressed hydrogen gas is conducted through conduits 35 and 37 into heater 31 where it is heated to about 1200 F. The heated hydrogen is removed from heater 3 1 through conduit 38 at about 5 pounds per square inch and a portion of it is conducted by conduit 39 into reactor 4 while the remaining portion is conducted through conduit 40 into reactor 9.

The unused portions of compressed hydrogen is conducted from conduit 35 through conduit 36 to supply hydrogen for extraneous utilization.

The flue gases from heater 31 are conducted through conduit 22 to compressor 23 and the compressed heated flue gases are then conducted into conduit 24. The flue gases in conduit 24 are divided so that a portion of these gases is conducted through conduit 26 into a coil in reactor 9 and the remaining portion of the flue gases is conducted through conduit 25 into a corresponding coil in reactor 4. The hot flue gases in the coils of the respective reactors 4 and 9 heat the interior reactor chamber and after losing their sensible heat they are conducted from the reactors 4 and 9 through respective conduits 28 and 27 to a common conduit 29. A portion of the relatively cold flue gas is vented from conduit 29 through conduit 32 to the atmosphere and the remaining portion of cold flue gas is conducted through conduit 30 back into the chamber of heater 31.

The embodiment of FIG. 2 shows the embodiment using a moving bed of catalysts. In this embodiment the paraflin feed stock is introduced through conduits 51 and 52 into a heater 85 heated by conventional means (not shown). The heated feed stock at about 1000 F. is

'vaporous and is conducted through conduit 53 into the bottom of reactor 54. The vapors flow upwardly in the reactor 54 whereas the suitable catalyst used moves downwardly and through the vapors, due to the force of gravity on the solid catalyst particles.

The reaction products are removed from reactor 54 through conduit 55 and are combined with the aromatic constituents in conduit 62 to flow through a common conduit 56 into a fractionation tower 63.

The heavy molecules at the bottom of fractionation column 63 are conducted through conduit 64 into an extraction column 65 where unreacted paraflins are separated from the newly formed aromatic constituents. The aromatic constituents are conducted through conduit 66 into the solvent recovery tower 67 and are then removed from the top of tower 67 through conduit 68 whereas the solvent used for extraction is conducted through conduit 69 back into the extraction column 65.

The gas in the top of fractionator 63 is conducted through conduit 71 into compressor 57 and thence through conduit 2 into a coil in heater $5. The gas heated up to 1300" F. in the coil is next conducted through conduit 58 into a soaking drum 59 where additional aromatic constituents are formed due to polymerization. The reaction products from drum 59 are conducted through conduit 60 into a separator 61 where hydrogen gas is separated from the polymers.

The hydrogen gas is removed from separator 61 through conduit 81. A portion of the hydrogen in conduit 81 is removed from the system through conduit 82 for external use. The remainder of the hydrogen in conduit 81 is conducted through conduit 83 into compressor 84 and thence through conduit 88 into a coil in heater 85 from which coil the heated compressed hydrogen gas is conducted into conduit 86 and through conduit 86 into reactor 54.

The flue gases from the regenerator reactor are conducted through conduit 73 from the top of the reactor 54 and are partly vented to the atmosphere through conduit 75 and partly passed through conduit 74 into compressor 76.

The flue gases after being compressed are conducted through conduit 77 into a lock chamber 78 of the catalyst lift line. The catalyst and flue gas pass through lock chamber 78 and are elevated through lift conduit 79 into reactor 54 and then to the catalyst regenerator 89 located at the top of reactor 54. Air-oxygen is admitted into lift conduit 79 through conduit 80 at a rate suitable to burn off carbon deposited upon the catalyst particles. At the top of the lift conduit 79 the catalyst separates from the lifting gases and falls due to gravity through the interior chamber of reactor 54.

FIG. 3 shows an embodiment showing the use of a fluidized bed of catalyst. In this embodiment the paraflin feed stock is introduced through conduit 101. The paraffin feed stock in conduit 101 is combined with recycled constituents in conduit and conducted through a common conduit 102 into a conventionally fired heater 135. The combined constituents are passed through a coil in heater 135.

From heater the heated parafiinic material is conducted through conduit 103 into the base of the reactor 104. The catalyst in a dense phase flows upwardly as it is lifted by the incoming vapor stream from conduit 103. The catalyst enters into stripper 108 through suitable slot openings located near the top thereof. Here the catalyst is stripped of its volatile material and then flows downwardly.

Compressed flue gas mixed with the proper proportion of air or oxygen then lifts the spent catalyst through lift conduit 107 to the regeneartor 137. During the elevation in the conduit to regenerator 137, the regeneration of the catalyst is effected. After regeneration the reactivated catalyst is recovered by means of a conventional cyclone separator located in container 137 and returned to reactor 104- through conduit 106. In this embodiment of the invention, the catalyst is circulated continuously between the reaction chamber and the regeneration zone. As shown in :FIG. 3, the catalyst lift conduit 107 as well as the catalyst return conduit 106 are located within the reactor 104. The heat of combustion of the carbon par- F. higher than the temperature of the reacting constituents.

The reaction products of reactor 104 leave through conduit 105 and enter into the liquid and gas separating drum 111. The separated liquid constituents are conducted through conduit 112 from drum 111 into fractionator 113. The constituents rich in aromatics from fractionator 113 are conducted through conduit 114 into the extractive distillation column 115 while the light hydrocarbon gases leave the top of fractionator 113 through conduit 121.

The heavy components from the column 115 are conducted through conduit 116 into the solvent recovery column 117. Here the desired aromatic components are recovered through conduit 118 and the solvent for extractive distillation is recycled from the bottom of column 117 back to column 115.

The hydrogen gas separated in drum 111 is conducted through conduit 130 to compressor 131. The compressed gas is conducted from conduit 132 partly for external use by way of conduit 133 and partly for recycle use through conduit 134 and a coil in heater 135 to conduit 136. The heated hydrogen gas is then conducted through conduit 136 into reactor 104.

Flue gas from the regenerator 137 is in part dischcarged to the atmosphere through conduit 138 and in part the flue gas is conducted through conduit 139 to compressor 140 whereupon the compressed flue gas is introduced into lift line 107.

The drawing of FIG. 4 shows an isothermal embodiment of this invention. The flue gas is removed from the convection chamber 152 of the heater 150 through conduit 153. It is compressed in compressor 154 and part of the compressed gas is recycled back to the radiant chamber 151 of the heater 150 through conduit 155 while the remainder of the compressed gas is conducted through conduit 156 partly through conduit 158 into the reactor heat ing jacket 165 and partly through conduit 157 into the base of the heating coil 66.

The heating jacket is a concentric cylindrical shell attached hermetically in spaced-relationship to the reactor 164. Bafiles (not shown) are installed between the jacket wall and the reactor wall to facilitate heat exchange. Other conventional means for increasing the heat transfer area both within the reactor as well as within the jacket chamber are operable.

The heating coil 166 preferably consists of longitudinal tubes or coils provided with fins. The flue gases leave the heating coils through conduit 159 and leave the jacket chamber through conduit 160 and combine into a common conduit 161. Part of the gas is vented into the atmosphere through conduit 162 and the remainder is cycled back into the conventional chamber 152 of the heater 150.

The isothermal reactor (FIG. 4) is employed in order to utilize the waste heat of flue gases to provide a uniform temperature gradient inside the reactor. The hot flue gases may be obtained from any conventionally fired heater or from the catalyst regeneration system. The reactor 164 contains the suitable catalyst and is provided with inlet and outlet aperture (not shown) for inlet of paraffinic feed stock and for outlet of the converted reaction products.

Examples of this invention are as follows:

Example I A parafiinie feed stock containing 95 percent normal hexane and having a boiling point range of 155 F. to 160 F. was vaporized and superheated to 950 F. The vapors were passed through a catalytic bed (FIG. 1) having an average temperature of about 950 F. and a space velocity of 0.3 volume liquid feed per volume of catalytic bed per hour. The residence time in contact with the catalyst was 30 seconds and the pressure used was atmospheric pressure.

No hydrogen recycle gas was used. The liquid product obtained was 60% (percent) benzene using platinum A paraflinic feed stock containing 99 percent by weight of normal heptane was vaporized and passed through the reactor under conditions identical to those of Example I. The liquid reaction product contained 40.10 percent by weight of toluene and 3.85 percent benzene. The catalyst used Was cobalt molybdate supported on activated alumina.

Example III A feed stock containing 99 percent normal octane was used under the reaction conditions stated in Example I except that inlet temperature was 20 F. higher than the reaction temperature. The catalyst used was platinum supported on alumina. The liquid reaction product contained 19.50 percent by weight ortho-xylene, 27.15 percent by Weight of ethyl benzene, 12.45 percent by weight of styrene, 3.65 percent by weight of toluene and 9.35 percent by weight of benzene. It has been found that chromium oxide, molybdenum oxide and cobalt molybdate are equally effective and the effect of these catalysts are promoted by the addition of neodymium oxide or didymium oxide.

Example IV An example of the preparation of a promoted catalyst is as follows:

A 358 gram sample of activated alumina was impregnated with a solution of 64.0 grams chromium oxide in 150 cc. of water. The impregnated alumina was dried in an air oven for 24 hours and then was mixed with a slurry made of 64 grams of neodymium oxide in cc. of acetone. The catalyst was dried at C. and then calcined at 500 C. in an atmosphere of hydrogen for three hours. The final catalyst composition had 11.7 percent by weight of chromium oxide and 12 percent neodymium oxide.

The neodymium oxide may be used in its pure or technically pure form.

The neodymium oxide may be used in the form of a mixture prepared from monazite sand and comprising, lanthanum oxide, neodymium oxide, praseodymium oxide, samarium oride and other rare earths including ytterbium oxide. The more plentiful and more inexpensive didymium oxide is operable in this invention and it is prepared by the removal of cerium from monazite by use of conventional procedure.

This invention is of generic scope and therefore not limited to the illustrative embodiments and examples shown and described.

We claim:

1. The process of dehydrocyclization of tertiary carbon atom free paraffinic compounds containing at least six carbon atoms in a straight chain comprising reacting said compounds at about atmospheric pressure and at from 840 F. to 1100 F. in the presence of platinum and a promoter selected from the group consisting of neodymium oxide and didymium oxide.

2. The process of claim 1 wherein said compounds are reacted in the presence of hydrogen.

3. The process of claim 1 wherein the catalyst is employed in a fluidized state and wherein a heat of regeneration of 1200 F. to 1300 F. is used to maintain said reaction temperature of 840 F. to 1100 F.

4. The process of dehydrocyclization of tertiary carbon atom free paraffinic compounds containing at least six carbon atoms in a straight chain comprising reacting said compounds at about atmospheric pressure and at from 840 F. to 1100 F. in the presence of cobalt molybdate which is promoted selectively by a substance selected from the group consisting of neodymium oxide and didymium oxide.

5. The process of claim 4 wherein said compounds are reacted in the presence of hydrogen.

6. The process of claim 4 wherein the cobalt molybdate is employed in a fluidized state and wherein a heat of regeneration of 1200 F. to 1300" F. is used to maintain said reaction temperature of 840 F. to 1100 F.

References Cited in the file of this patent UNITED STATES PATENTS Morrell et a1 Feb. 21, 1939 Greensfelder et a1 Dec. 21, 1943 Bannerot July 22, 1952 Schrnetterling et al. Mar. 12, 1957 Viles Aug. 18, 1959 

1. THE PROCESS OF DEHYDROCYCLIZATION OF TERTIARY CARBON ATOM FREE PARAFFINIC COMPOUNDS CONTAINING AT LEAST SIX CARBON ATOMS IN A STRAIGHT CHAIN COMPRISING REACTING SAID COMPOUNDS AT ABOUT ATMOSPHERIC PRESSURE AND AT FROM 840*F. TO 1100*F. IN THE PRESENCE OF PLATINUM AND A PROMOTER SELECTED FROM THE GROUP CONSISTING OF NEODYMIUM OXIDE AND DIDYMIUM OXIDE. 